Methods and apparatus for latch-up free boosting

ABSTRACT

A voltage generator includes a boosting circuit boosting a power voltage to generate first through fourth voltages, and a boosting controller controlling the boosting circuit. The boosting controller sets the third and fourth voltages to a voltage level lower than that of a ground voltage while the first and second voltages are generated, so that a plurality of voltages may be stably generated, i.e., without latch-up.

CROSS REFERENCE TO RELATED APPLICATION

This is a divisional application based on pending application Ser. No.11/826,374, filed Jul. 13, 2007, the entire contents of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to methods and apparatus forboosting a voltage when power is turned on (“power-on”). Moreparticularly, embodiments of the invention relate to latch-up freevoltage boosting methods and apparatuses for stably boosting voltageswithout triggering latch-up.

2. Description of the Related Art

Generally, a peculiar state called latch-up may occur in a device havinga complementary metal oxide semiconductor (CMOS) structure. Latch-up isa parasitic phenomenon that may occur when a parasitic thyristor, e.g.,silicon controlled rectifier (SCR), at a PNPN junction inherentlyexisting in a CMOS chip causes over-current to flow. Depending on thecircuitry, the amount of current produced may be large enough topermanently destroy a chip including the CMOS structure. Latch-upgenerally occurs when input and output voltages exceed a rated level sothat large current flows through an internal component, or when a powervoltage exceeds the rated level so that the internal component fallsinto a breakdown state. Once the chip falls into a latch-up state, thelatch-up state may be continuously maintained until power is turned off(“power-off”) due to the structure of the thyristor. Therefore, the chipmay be permanently destroyed.

To perform a variety of functions, the CMOS chip may be designed suchthat it operates using voltages of various levels. When power isinitially supplied to the CMOS chip from the outside, the CMOS chip maygenerate various voltages to be used inside the CMOS chip in sequence orin parallel by boosting a power voltage provided from the outside. Whenthe voltages applied to respective terminals of the PNPN junction aredifferent from one another, latch-up may occur according to the sequencein which the various voltages are applied to the respective terminals.

SUMMARY OF THE INVENTION

Embodiments of the present invention are therefore directed to methodsand apparatus employing a latch-up free boosting scheme, whichsubstantially overcome one or more of the problems due to thelimitations and disadvantages of the related art.

It is therefore a feature of an embodiment of the present invention toprovide latch-up free boosting methods capable of stably generating aplurality of voltages without triggering latch-up.

It is therefore a separate feature of an embodiment of the presentinvention to provide latch up free boosting apparatus, which are capableof stably generating a plurality of voltages without triggeringlatch-up.

It is therefore a separate feature of an embodiment of the presentinvention to provide a voltage generator that may variably control atime taken for the substrate voltage to be set to a voltage lower than aground voltage at power-on.

At least one of the above and other features and advantages of thepresent invention may be realized by providing a boosting method,including receiving a power voltage, boosting the power voltage togenerate a first voltage, boosting the first voltage to generate asecond voltage, and generating a third voltage that is a negativevoltage of the second voltage, wherein the third voltage is set to avoltage level lower than that of a ground voltage while the first andsecond voltages are generated.

The third voltage may be a substrate voltage. The third voltage may be anegative voltage of the power voltage while the first and secondvoltages are generated.

A time taken for the third voltage to be set to a negative voltage ofthe power voltage while the first and second voltages are generated maybe controlled.

At least one of the above and other features and advantages of thepresent invention may be realized by providing a voltage generator,including a boosting circuit boosting a power voltage to generate firstthrough fourth voltages, and a boosting controller controlling theboosting circuit such that the third and fourth voltages are set to avoltage level lower than that of a ground voltage while the first andsecond voltages are generated.

The boosting circuit may include a first booster boosting the powervoltage to generate the first voltage, a second booster receiving thepower voltage, the first voltage and the fourth voltage to generate thesecond and third voltages, and a third booster receiving the powervoltage to generate the fourth voltage.

The boosting controller may generate first and second control signalsfor controlling the second booster, and may generate a third controlsignal for controlling the third booster. The second booster may includea first boosting unit generating a fifth voltage lower than the groundvoltage.

The second booster may further include a first switching unit outputtingthe fifth voltage as the third voltage in response to the first andsecond control signals. The first switching unit may apply the fifthvoltage to the substrate in response to the first control signal. Thesecond booster may further include a second switching unit transmittingthe fifth voltage applied to the substrate as the third voltage inresponse to the second control signal.

The second booster may further include a third switching unittransmitting the fifth voltage as the fourth voltage in response to thethird switching control signal. The first through third switchingcontrol signals may be sequentially activated at predeterminedintervals.

The first and second switching control signals may be simultaneouslyactivated, and the third switching control signal may be activated aftera lapse of a predetermined time from when the first and second switchingcontrol signals are simultaneously activated. The first through thirdswitching control signals may be simultaneously activated. The secondbooster may further include a second boosting unit receiving the powervoltage and the first voltage to generate the second voltage. The secondbooster may further include a third boosting unit receiving the powervoltage and the second voltage to generate the third voltage.

At least one of the above and other features and advantages of thepresent invention may be realized by providing a liquid crystal displaydevice, including a liquid crystal panel displaying an image, and avoltage generator receiving a power voltage to generate first throughfourth voltages for driving the liquid crystal panel, wherein thevoltage generator includes a first booster boosting the power voltage togenerate the first voltage, a second booster receiving the powervoltage, the first voltage and the fourth voltage to generate the secondand third voltages, a third booster receiving the power voltage togenerate the fourth voltage, and a controller controlling the second andthird boosters such that the third and fourth voltages are set to avoltage level lower than that of a ground voltage while the first andsecond voltages are generated.

The first voltage may be an internal power voltage, the second voltagemay be a gate-on voltage for driving gate lines of the liquid crystalpanel, the third voltage may be a gate-off voltage for driving the gatelines of the liquid crystal panel, and the fourth voltage may be avoltage for generating a common voltage supplied to the liquid crystalpanel. The controller may generate first and second control signals forcontrolling the second booster, and may generate a third control signalfor controlling the third booster.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become more apparent to those of ordinary skill in the art bydescribing in detail exemplary embodiments thereof with reference to theattached drawings, in which:

FIG. 1 illustrates a block diagram of a voltage generator according toan exemplary embodiment of the present invention;

FIG. 2 illustrates a block diagram of a voltage generator according toanother exemplary embodiment of the present invention;

FIG. 3 illustrates a diagram of first through fourth voltages generatedfrom first through third boosting circuits of FIG. 2;

FIG. 4A illustrates a schematic view of sections of NPN and PNPtransistors;

FIG. 4B illustrates an equivalent circuit diagram of the NPN and PNPtransistors of FIG. 4A;

FIG. 5 illustrates a diagram of voltages generated from the voltagegenerator of FIG. 2 according to an exemplary embodiment of the presentinvention;

FIG. 6 illustrates a circuit diagram of an embodiment of the second andthird boosting circuits of FIG. 2;

FIGS. 7 through 9 illustrate timing diagrams of various exemplaryembodiments of switching control signals;

FIG. 10 illustrates a block diagram of a liquid crystal display deviceincluding a voltage generator according to an exemplary embodiment ofthe present invention; and

FIG. 11 illustrates a block diagram of an embodiment of the voltagegenerator of FIG. 10 according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

Korean Patent Application No. 10-2006-95920, filed on Sep. 29, 2006, inthe Korean Intellectual Property Office, and entitled: “Latch-Up FreeBoosting Scheme,” is incorporated by reference herein in its entirety.

Embodiments of the present invention will now be described more fullyhereinafter with reference to the accompanying drawings, in whichexemplary embodiments of the invention are illustrated. Embodiments ofthe invention may, however, be embodied in different forms and shouldnot be construed as limited to the exemplary embodiments set forthherein. Rather, these exemplary embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the invention to those skilled in the art.

In the figures, the dimensions of layers and regions may be exaggeratedfor clarity of illustration. It will also be understood that when anelement is referred to as being connected to another element or betweentwo elements, the element may be directly connected to the other elementor directly between the two other elements and/or one or moreintervening elements may be present. Like reference numerals refer tolike elements throughout the specification.

FIG. 1 illustrates a block diagram of a voltage generator according toan exemplary embodiment of the present invention. Referring to FIG. 1,the voltage generator 100 may include a boosting controller 110 and aboosting circuit 120. The boosting controller 110 may generate controlsignals for controlling the boosting circuit 120 in response to apower-on signal P_ON. The boosting circuit 120 may receive a powervoltage VCI to generate first through fourth boosting voltages AVDD,VGH, VGL and VCL in response to the control signals of the boostingcontroller 110. The first through fourth boosting voltages AVDD, VGH,VGL and VCL may be used in an electronic device including the voltagegenerator 100, e.g., a computer system, a liquid crystal display device,a personal multimedia player (PMP), a mobile phone, an MP3 player, anaudio system, etc. Although the exemplary embodiment illustrated in FIG.1 illustrates the boosting circuit 120 as generating the first throughfourth boosting voltages AVDD, VGH, VGL and VCL, embodiments of theinvention are not limited thereto. For example, a number and level ofeach voltage generated by the boosting circuit 120 may be variouslymodified depending on specifications required in electronic devices.

FIG. 2 illustrates a block diagram of a voltage generator according toanother exemplary embodiment of the present invention.

Referring to FIG. 2, the voltage generator 200 may include an internalvoltage generator 205, first through third boosting circuits 210, 220,230, and a boosting controller 240. The boosting controller 240 maygenerate switching control signals P32, P33 and P44 for controlling thesecond and third boosting circuits 220 and 230 in response to thepower-on signal P_ON. The internal voltage generator 205 may receive thepower voltage VCI to generate an internal power voltage VCI1.

The first boosting circuit 210 may include a first boosting unit 212 andcapacitors C11 and C12. The capacitor C11 may be connected to the firstboosting unit 212 through terminals C11P and C11N, and the capacitor C12may be connected to the first boosting unit 212 through a terminal C12P.The first boosting circuit 210 may receive the internal power voltageVCI1 to output the first boosting voltage AVDD to the terminal C12P.

The second boosting circuit 220 may include a second boosting unit 222and capacitors C21, C22, C23 and C24. The capacitor C21 may be connectedto the second boosting unit 222 through terminals C21P and C21N, and thecapacitor C22 may be connected to the second boosting unit 222 throughterminals C22P and C22N. One end of the capacitor C23 may be connectedto the second boosting unit 222 through a terminal C23P, and one end ofthe capacitor C24 may be connected to the second boosting unit 222through a terminal C24P. Other ends of the capacitors C23 and C24 may beconnected to a ground voltage, respectively. The second boosting circuit220 may receive the internal power voltage VCI1, the first voltage AVDDof the first boosting circuit 210, and the fourth boosting voltage VCLof the third boosting circuit 230, and may output second and thirdboosting voltages VGH and VGL to the respective terminals C23P and C24Pin response to control signals P32 and P33.

The third boosting circuit 230 may include a third boosting unit 232 andcapacitors C31 and C32. One end of the capacitor C31 may be connected tothe third boosting unit 232 through a terminal C31P, and the capacitorC32 may be connected to the third boosting unit 232 through terminalsC32P and C32N. The third boosting circuit 230 may receive the internalpower voltage VCI1 to generate the fourth boosting voltage VCL to theterminal C31P in response to the switching control signal P44 providedfrom the boosting controller 240.

The second boosting circuit 220 may receive the internal power voltageVCI1, the first boosting voltage AVDD of the first boosting circuit 210,and the fourth boosting voltage VCL of the third boosting circuit 230 togenerate the second and third boosting voltages VGH and VGL. When thefourth boosting voltage VCL is supplied to the second boosting unit 222before it is not sufficiently stabilized to a normal voltage level,latch-up may occur in the second boosting unit 222.

FIG. 3 illustrates a diagram of waveforms of first through fourthboosting voltages AVDD, VGH, VGL and VCL that may be generated fromfirst through third boosting circuits 210, 220, 230 of FIG. 2. Asdescribed above, in some embodiments, the first boosting circuit 210 mayboost the internal power voltage VCI1 to output the first boostingvoltage AVDD.

The second boosting circuit 220 may receive the internal power voltageVCI1, the first boosting voltage AVDD and the fourth boosting voltageVCL to generate the second and third boosting voltages VGH and VGL. Moreparticularly, the second boosting circuit 220 may boost the firstboosting voltage AVDD to a negative voltage to thereby generate thethird boosting voltage VGL. As shown in FIG. 3, the third boostingvoltage VGL may not be generated until the internal power voltage VCI1and the first and second boosting voltages AVDD and VGH are generated,e.g., the third boosting voltage VGL may be generated after the internalpower voltage VCI1, and the first and second boosting voltages AVDD andVGH are generated. Thus, the terminal C24P may be in a floating state orconnected to a Schottky diode (not shown). Referring to FIG. 3, in suchcases in which the second boosting voltage VGH may be set to a desiredlevel after the internal power voltage VCI1 is set, there is apossibility that latch-up may occur in the second boosting circuit 220,as described in more detail below.

FIG. 4A illustrates a schematic view of sections of NPN and PNPtransistors; and FIG. 4B illustrates an equivalent circuit diagram ofthe NPN and PNP transistors of FIG. 4A.

Referring to FIGS. 4A and 4B, the third boosting voltage VGL may be asubstrate bias voltage. When power is on, the internal power voltageVCI1 and the first and second boosting voltages AVDD, VGH may begenerated by the voltage generator 200 in the following order: theinternal power voltage VCI1, the first voltage AVDD, and the secondvoltage VGH, as illustrated in FIG. 3. When an emitter voltage of a PNPtransistor Q1 is greater than a base voltage thereof, an emitter currentflows to the collector of the PNP transistor Q1. Since the emitter ofthe PNP transistor Q1 may be connected to the input voltage, e.g.,internal power voltage VCI1, and the base may be in a floating statebefore boosting, an emitter-base voltage may be a forward bias voltage,i.e., V_(E)=V_(BE)≈0.7V, and the emitter current may be expressed asI_(E)=(VCI1−V_(E))/R1 provided that an initial voltage is set to 0V. Acollector voltage of the PNP transistor Q1 may be expressed asV_(C)=VGL+Ie4*R4, and thus, V_(C) will be a positive voltage if|VGL|<|Ie4*R4|. Therefore, the positive collector voltage V_(C) of thePNP transistor Q1 may enable an NPN transistor Q2 to be turned on.Likewise, an NPN transistor Q3 may also be turned on. As the NPNtransistors Q2 and Q3 are turned on, a current path may be formedbetween the second boosting voltage VGH and the ground voltage VSS. As aresult, latch-up may occur because the PNP transistor Q1 and the NPNtransistors Q2 and Q3 may all be turned on.

As described above, if latch-up occurs due to, e.g., instant forwardbiasing at power-on, the semiconductor chip will generally, if notalways, need to be discarded, i.e., be permanently damaged. To preventand/or reduce latch-up, a Schottky diode (not shown) may be connectedbetween the third boosting voltage VGL and the ground voltage VSS, e.g.,to terminal C24P shown in FIG. 2. However, employing a Schottky diodemay increase a fabrication cost of a semiconductor chip, and may furtherlead to a problem that the Schottky diode may be destroyed if adifference between the emitter voltage of the NPN transistor Q2 and thethird voltage VGL becomes great.

In the voltage generator 200 according to the exemplary embodiment ofthe present invention, the third boosting voltage VGL may be set to anegative level lower than the ground voltage VSS, e.g., −VCI1 (i.e.,negative internal power voltage), so that the NPN transistors Q2 and Q3are not turned on. That is, if |VGL|>|Ie4*R4|, the collector voltageV_(C) there may be a negative (minus) voltage. Accordingly, the NPNtransistor Q2 may not be turned on.

FIG. 5 illustrates an exemplary diagram of voltages generated from thevoltage generator 200 of FIG. 2 according to an exemplary embodiment ofthe present invention. Referring to FIG. 5, the third and fourthboosting voltages VGL and VCL may be set to the negative internal powervoltage −VCI1 at the same time as, e.g. when the internal power voltageVCI1 is generated. Therefore, referring to FIGS. 4 and 5, thetransistors Q2 and Q3 may not be turned on before the second voltage VGHis set to a desired level. Consequently, in such exemplary embodiments,latch-up may be reduced and/or prevented.

FIG. 6 illustrates a circuit diagram of an embodiment of the second andthird boosting circuits 220, 230 of FIG. 2. The second and thirdboosting circuits 220 and 230 of FIG. 6 are exemplary embodiments, andthus, embodiments of the invention are not limited thereto. Moreparticularly, e.g., various modifications may be made thereto forgenerating the second through fourth voltages VGH, VGL and VCL.

Referring to FIG. 6, the second boosting circuit 220 may includecapacitors C21, C22, C23 and C24, and a plurality of switches SW21,SW23, SW24, SW25, SW26, SW27, SW29, SW30, SW31, SW32, SW33. The thirdboosting circuit may 230 include capacitors C31 and C32, and a pluralityof switches SW41, SW42, SW43, and SW44. The switching control signalsP1, P2, P3, P4, P32, P33 and P44 may be provided from the boostingcontroller 240 of FIG. 2 to control ON/OFF operation of the switchesSW21, SW23, SW24, SW25, SW26, SW27, SW29, SW30, SW31, SW32, SW33, SW41,SW42, SW43 and SW44. FIGS. 7 through 9 illustrate timing diagrams ofvarious exemplary embodiments of switching control signals P1, P2, P3,P4, P32, P33 and P44.

Referring to FIGS. 6 and 7, when the switches SW21 and SW26 are turnedon in response to the switching control signal P1, the terminal C21P maybe charged to a voltage corresponding to a voltage difference betweenthe first and fourth boosting voltages, i.e., AVDD−VCL. When theswitches SW24, SW27 and SW29 are turned on in response to the switchingcontrol signal P2, a voltage of the terminal C22P may increase to avoltage corresponding to a voltage difference between twice the firstboosting voltage and the fourth boosting voltage, i.e., 2AVDD−VCL, dueto the capacitor C21. When the switches SW25 and SW30 are turned on inresponse to the switching control signal P4, a voltage of the terminalC23P may increase to a voltage corresponding to a difference betweenthree times the first boosting voltage and the fourth boosting voltage,i.e., 3AVDD−VCL. Therefore, the second voltage VGH, i.e., the voltage ofthe terminal C23P, may be 3AVDD−VCL. In some embodiments of theinvention, if the voltage connected to the switches SW27 and SW30 is/arechanged to other voltages, e.g., the internal power voltage VCI1 insteadof the first boosting voltage AVDD, the voltage level of the secondvoltage VGH may be variously modified.

When the switches SW23 and SW31 are turned on in response to theswitching control signal P3, the third boosting voltage VGL may beapplied to the terminal C24P through the switch SW32, and may correspondto −(2AVDD−VCL+VCI1). In embodiments of the invention, the thirdboosting voltage VGL applied to the terminal C24P may be changed byvarying the voltages applied to respective terminals of the switchesSW23 and SW30.

Meanwhile, charges may be accumulated in the capacitor C32 in responseto the control signals P1 and P2 from a time when the power-on signalP_ON is activated. When the switch SW33 is turned on in response to theswitching control signal P33, a substrate voltage VSUB may be set to thenegative internal power voltage −VCI1. As described above, latch-up mayoccur at a PNPN junction, and thus, may occur at the terminals C22P andC22N of FIG. 6 (see FIG. 4A). In the embodiment of the presentinvention, however, the substrate voltage VSUB is set to the negativeinternal power voltage −VCI1 lower than the ground voltage VSS from thetime when power is turned on, which makes it possible to prevent and/orreduce latch-up. Subsequently, when the switch S32 is turned on inresponse to the switching control signal P32, the voltage of theterminal C24P, i.e., the third voltage VGL, may be set to the negativeinternal power voltage −VCI1. Afterwards, when the switch SW33 is turnedoff in response to the switching control signal P33 of low level, andthe switch SW44 is turned on in response to the switching control signalP44 of high level, the fourth voltage VCL applied to the terminal C31Pmay be set to the negative internal power voltage −VCI1 .

FIGS. 8 and 9 are timing diagrams illustrating various embodiments ofswitching control signals P32, P33 and P44. Referring to FIGS. 6 and 8,in embodiments in which the activation transition point of the switchingcontrol signal P32 is set to be the same as that of the switchingcontrol signal P33, the third voltage VGL may be set to the negativeinternal power voltage −VCI1 simultaneously with the substrate voltageVSUB. Alternatively, referring to FIGS. 6 and 9, in embodiments in whichthe activation transition points of the switching control signals P32and P44 are set to be the same as that of the switching control signalP33, the third voltage VGL and the fourth voltage VCL may set to thenegative internal power voltage −VCI1 simultaneously with the substratevoltage VSUB.

Since three capacitors C_(SUB), C24 and C31 may be charged by thecurrent supplied from the internal voltage generator 205 of FIG. 2, theamount of current may increase. When the time(s) at which that the thirdand fourth voltages VGL and VCL are set to the negative internal powervoltage −VCI1 are set to be the same as that of the substrate voltageV_(SUB) as illustrated in FIGS. 8 and 9, it generally takes a lot oftime for the substrate voltage V_(SUB) to reach a target voltage, i.e.,the negative internal power voltage −VCI1. However, since an equivalentcapacitance appearing in the substrate SUB becomes enormously large, thevoltage rise caused by leakage current may be prevented more effectivelythan when the signals illustrate in FIG. 7 are employed. In other words,in embodiments of the invention, it is possible to selectively designactivation transition points of the switching control signals P33, P32and P44 in consideration of trade-off relationship, depending on whetherit is desired to rapidly lower the substrate voltage VSUB (as shown inFIG. 7), or prevent the voltage rise of the substrate voltage VSUBcaused by the inflow of external leakage current (as shown in FIG. 8,C_(TOT)=C_(SUB)+C₂₄).

FIG. 10 illustrates a block diagram of a liquid crystal display device(LCD) 1000 including a voltage generator according to an exemplaryembodiment of the present invention.

Referring to FIG. 10, the LCD 1000 may include a timing controller 1010,a source driver 1020, a voltage generator 1030, a gate driver 1040, anda liquid crystal panel 1050.

The liquid crystal panel 1050 may include a plurality of gate linesG1-Gn, a plurality of source lines S1-Sm crossing the plurality of gatelines G1-Gn, and a plurality of pixels arranged in regions defined bythe gate lines and data lines. Each of the pixels may include a thinfilm transistor (TFT) T1 of which gate and source electrodes may berespectively connected to the gate line and the data line, a liquidcrystal capacitor C_(LC) connected to a drain electrode of the TFT T1,and a storage capacitor C_(ST). In such a pixel structure, when the gatelines G1-Gn are sequentially selected by the gate driver 1040 and apulse type gate-on voltage is applied to the selected gate line, the TFTT1 of the pixel connected to the selected gate line may be turned on,and a voltage containing pixel information may then be applied to eachof the data lines by the source driver 1020. This voltage may be appliedto the liquid crystal capacitor C_(LC) and the storage capacitor C_(ST)through the TFT in the corresponding pixel to drive the liquid andstorage capacitors C_(LC) and C_(ST). Thus, a predetermined displayoperation can be performed.

The timing controller 1010 may receive a current pixel data signal RGB,a horizontal synchronization signal H_SYNC, a vertical synchronizationsignal V_SYNC, a clock signal MCLK, and a data enable signal DE, whichmay be inputted from external devices. The timing controller 1010 mayoutput a pixel data signal RGB′ and control signals to the source driver1020, wherein a data format of the pixel data signal RGB′ may beconverted to meet interface specification(s) with the source driver1020. The control signals supplied to the source driver 1020 from thetiming controller 1010 may include a latch signal TP, a start horizontalsignal STH, and a horizontal clock signal HCLK.

The voltage generator 1030 may receive the power voltage VCI from theoutside to generate a variety of voltages required for the operation ofthe LCD 1000, e.g., a gate-on voltage VGH (e.g., the second boostingvoltage), a gate-off voltage VGL (e.g., the third boosting voltage), ananalog power voltage AVDD (e.g., the first boosting voltage), a gate-oncommon voltage VCOMH, and a gate-off common voltage VCOML. The gate-onvoltage VGH and the gate-off voltage VGL may be supplied to the gatedriver 1040, and the analog power voltage AVDD may be used as anoperational voltage of the LCD 1000.

The gate driver 1040 may sequentially scan the gate lines G1-Gn of theliquid crystal panel 1050 in response to the control signals, i.e., astart vertical signal STV, a gate clock signal GCLK, and an outputenable signal OE, supplied from the timing controller 1010. Scanning maybe an operation for sequentially applying the gate-on voltage VGH to thegate lines to enable the pixel of the gate line to which the gate-onvoltage VGH is applied to be in a state that data can be writtenthereto.

The source driver 1020 may be responsive to the control signals, i.e.,the latch signal TP, the start horizontal signal STH and the horizontalclock signal HCLK, supplied from the timing controller 1010, to therebydrive the data lines D1-Dm of the liquid crystal panel 1050 withgradation voltages corresponding to the pixel data signals RGB′ among aplurality of gradation voltages generated from a gradation voltagegenerator (not shown).

FIG. 11 illustrates a block diagram of an embodiment of the voltagegenerator 1030 of FIG. 10 according to an exemplary embodiment of thepresent invention. Referring to FIG. 11, the voltage generator 1030 mayinclude a voltage generation unit 1031 and a common voltage generator1032.

The voltage generation unit 1031 may receive the power voltage from theoutside to generate the common voltage VCL, the gate-on voltage VGH, thegate-off voltage VGL and the analog power voltage AVDD. Here, the commonvoltage VCL may be supplied to the common voltage generator 1032, andthe gate-on voltage VGH and gate-off voltage VGL may be used in the gatedriver 1040. The common voltage generator 1032 may receive the powervoltage VCI, the common voltage VCL and the analog power voltage AVDDgenerated by the voltage generation unit 1031, and may generate thegate-on common voltage VCOMH and the gate-off common voltage VCOML to besupplied to the common electrode of the capacitors C_(LC) and C_(ST) inthe liquid crystal panel 1050. Detailed constitution and operation ofthe voltage generation unit 1031 may be the same as those illustrated inFIGS. 2 through 9 and their corresponding descriptions.

The LCD 1000 according to the exemplary embodiment of the presentinvention may include the voltage generator 1030 for generating avariety of voltages required for operations, and the voltage generator1030 may stably generate voltages without latch-up.

According to embodiments of the present invention, a voltage generatorcan stably generate a plurality of voltages without latch-up because asubstrate voltage is set to a voltage lower than a ground voltage atpower-on.

Embodiments of the invention may separately provide a voltage generatorthat may variably control a time taken for the substrate voltage to beset to a voltage lower than a ground voltage at power-on.

The above-disclosed subject matter is to be considered illustrative, andnot restrictive, and the appended claims are intended to cover all suchmodifications, enhancements, and other embodiments, which fall withinthe true spirit and scope of the present invention. More particularly,exemplary embodiments of the present invention have been disclosedherein, and although specific terms are employed, they are used and areto be interpreted in a generic and descriptive sense only and not forpurpose of limitation. Accordingly, it will be understood by those ofordinary skill in the art that various changes in form and details maybe made without departing from the spirit and scope of the presentinvention as set forth in the following claims. Thus, to the maximumextent allowed by law, the scope of the present invention is to bedetermined by the broadest permissible interpretation of the followingclaims and their equivalents, and shall not be restricted or limited bythe foregoing detailed description.

What is claimed is:
 1. A voltage generator, comprising: a boosting circuit boosting a power voltage to generate first through fourth voltages; and a boosting controller controlling the boosting circuit such that the third and fourth voltages are set to a first voltage level lower than that of a ground voltage before the first and second voltages are generated wherein the boosting circuit comprises: a first booster boosting the power voltage to generate the first voltage; a second booster receiving the power voltage, the first voltage and the fourth voltage to generate the second and third voltages; and a third booster receiving the power voltage to generate the fourth voltage; wherein the boosting controller generates first and second control signals for controlling the second booster, and generates a third control signal for controlling the third booster; wherein the second booster comprises a first boosting unit generating a fifth voltage lower than the ground voltage; wherein the second booster further comprises a first switching unit outputting the fifth voltage as the third voltage in response to the first and second control signals; wherein the first switching unit applies the fifth voltage to a substrate in response to the first control signal; and wherein the second booster further comprises a second switching unit transmitting the fifth voltage applied to the substrate as the third voltage in response to the second control signal.
 2. The voltage generator as claimed in claim 1, wherein the second booster further comprises a second boosting unit receiving the power voltage and the first voltage to generate the second voltage.
 3. The voltage generator as claimed in claim 1, wherein the boosting controller further controls the boosting circuit such that the third voltage is set to a second voltage level lower than the first voltage level after the first and second voltages are generated.
 4. A liquid crystal display device, comprising: a liquid crystal panel displaying an image; and a voltage generator receiving a power voltage to generate first through fourth voltages for driving the liquid crystal panel, wherein the voltage generator, includes: a first booster boosting the power voltage to generate the first voltage; a second booster receiving the power voltage, the first voltage and the fourth voltage to generate the second and third voltages; a third booster receiving the power voltage to generate the fourth voltage; and a controller controlling the second and third boosters such that the third and fourth voltages are set to a voltage level lower than that of a ground voltage before the first and second voltages are generated wherein the controller generates first and second control signals for controlling the second booster, and generates a third control signal for controlling the third booster; wherein the second booster comprises a first boosting unit generating a fifth voltage lower than the ground voltage; wherein the second booster further comprises a first switching unit outputting the fifth voltage as the third voltage in response to the first and second control signals; wherein the first switching unit applies the fifth voltage to a substrate in response to the first control signal; and wherein the second booster further comprises a second switching unit transmitting the fifth voltage applied to the substrate as the third voltage in response to the second control signal.
 5. The liquid crystal display device as claimed in claim 4, wherein the first voltage is an internal power voltage, the second voltage is a gate-on voltage for driving gate lines of the liquid crystal panel, the third voltage is a gate-off voltage for driving the gate lines of the liquid crystal panel, and the fourth voltage is a voltage for generating a common voltage supplied to the liquid crystal panel.
 6. The liquid crystal display device as claimed in claim 4, wherein the controller further controls the second booster such that the third voltage is set to a second voltage level lower than the first voltage level after the first and second voltages are generated. 